1. Field of the Invention
The present disclosure relates to an antenna apparatus including a dipole antenna, and a wireless communication apparatus including the antenna apparatus.
2. Description of the Related Art
Background Art
A slot antenna has been known as an end-fire antenna according to a prior art. The slot antenna apparatus has a slot, which is formed at an edge of a ground conductor formed on a top surface of a dielectric substrate to intersect the edge, and a feeder line, which is formed on a reverse side of the dielectric substrate to intersect the slot. The feeder line is electromagnetically coupled to the slot, and a high-frequency signal transmitted via the feeder line excites the slot. In this case, an electric field appearing in the slot is guided along the slot in an edge direction of the dielectric substrate, and is radiated in an end-fire direction.
Most end-fire antennas are traveling-wave antennas, and therefore, it is generally easy to achieve a wide band. For example, in Patent Document 1, the band of a slot antenna is widened by devising the shape of a feeder line. In addition, there has been known a technique for raising the gain of an end-fire antenna by an antenna having an array structure including a plurality of slots, or by a tapered slot antenna including a tapered slot having a tapered shape (See Patent Document 2). Prior art documents related to the present disclosure are listed below:    Patent Document 1: Japanese Patent Laid-open Publication No. 2008-283251;    Patent Document 2: Japanese Patent Laid-open Publication No. 2009-5086;    Patent Document 3: U.S. Patent Application No. 2009/0195460;    Patent Document 4: U.S. Patent Application No. 2009/0046019;    Patent Document 5: U.S. Patent Application No. 2009/0207088; and    Patent Document 6: U.S. Pat. No. 6,281,843.
However, when a slot antenna that radiates radio waves in an edge direction of a dielectric substrate is applied to radio waves in a very high frequency band such as a millimeter-wave band, the following two problems arise. First of all, there is such a problem that it is difficult to form a feed portion for feeding to a slot to be small according to the wavelength of radio waves in the millimeter-wave band, by a general etching process of a printed wiring substrate. In addition, there is such a problem that loss of a ground current flowing along the slot becomes relatively large. Since the loss of the ground current is directly associated with a reduction in radiation efficiency, this problem cannot be solved even by the above-described antenna having the array structure or the tapered slot antenna.